Added runtime checks for GetClientRect errors. I noticed that if the window handle is invalid, the resulting rect will be uninitialized. This change makes it fail immediately. Review URL: http://codereview.appspot.com/2009042 git-svn-id: https://angleproject.googlecode.com/svn/trunk@386 736b8ea6-26fd-11df-bfd4-992fa37f6226